Effect of convergent–divergent flow on thermal and crystallization properties of PP/MWCNTs nanocomposites

Abstract

A melt-mixing process based on convergent-divergent flow has been used to prepare PP/MWCNT composites with a selfbuilt convergent-divergent die (C-D die) composed of different numbers of convergent plates. Dynamic extensional deformation was generated in the C-D die, which improved the mixing effect and mixing efficiency of the composites during extrusion. The C-D die acted as a mixer for composites when mounted onto a capillary rheometer. The residence time of PP/MWCNTs melt in the extensional flow field is adjusted by changing the numbers of convergent plates and the velocity of the ram. The intensity of extensional flow field is controlled by the structure of the convergent plate and the ram velocity. Influences of convergent-divergent flow on PP/ MWCNTs composites were characterized in terms of transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). TEM results showed that MWCNTs disperse more homogeneously with the increase of convergent plates. DSC showed that the crystallinity of PP/MWCNTs composites increased and the crystallization temperature shifted to higher temperature with the increase of the numbers of the convergent plates. TGA showed that the thermal stability of composites improved remarkably. The decomposition temperature increases from 381 to 408.28C when the numbers of convergent plates increased from 2 to 8. In addition, the increase of ram velocity also has the same influences on the dispersion of MWCNTs in the resin and the properties of PP/MWCNTs nanocomposites.

Dispersion of carbon nanotubes in ultrahigh‐molecular‐weight polyethylene by melt mixing dominated by elongation stress

“…The mixing unit is composed of a mixing stator, one long vane and part of the rotor. The structure and working principle of the feeding unit and the mixing unit were introduced in detail in our previous studies . The feeding unit and the mixing unit are connected with a baffle.…”

“…As shown in Figs and , the materials suffer dynamic elongation stress generated by the periodically changing volume of the mixing chamber which is expected to contribute significantly to dispersive mixing. These results are in accordance with those of our earlier studies . From Figs (a) and (b), individual CNTs can be found in the matrix with few entangled CNT clusters when the CNT loading is low.…”

A modified blister mixing element for generating extensional flow in a twin‐screw extruder: Process characterization and dispersion state of carbon nanotubes in cyclo‐olefin polymer

“…Unique mixing devices that generate extensional flows along the extrusion direction can improve the dispersion state by decreasing the contraction ratio in C-D geometry [6] and increasing the flow rate and number of extensional flows or residence time. [7][8][9][10] However, few studies have focused on generating extensional flow inside the barrel of a TSE by modifying the geometry of the element because these mixing devices are add-on units to the outlet of extruders or stand-alone devices.…”

Short‐time fabrication of well‐mixed high‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blends under elongational flow: morphology, mechanical properties and mechanism

“…capillary die and hyperbolic die) on the mixing and properties of polymer or polymer‐based composites, suggesting that elongational flow afforded not only the good dispersion or exfoliation of fillers but also the orientation of macromolecular chains and fillers, which improved the mechanical properties. We previously reported that elongational flow provided uniform dispersion of immiscible blends that exhibited good mech0061nical properties …”